Many food products that are prepared for human and/or animal consumption contain unwanted and potentially dangerous biological contaminants or pathogens, such as, for example, microorganisms, viruses, bacteria, (including inter- and intracellular bacteria, such as mycoplasmas, ureaplasmas, nanobacteria, chlamydia, rickettsias), yeasts, molds, fungi, prions or similar agents. Consequently, it is of utmost importance that these biological contaminants or pathogens be inactivated before the food product is used. This is especially critical when the material is to be administered to an infant or to a patient that has an immune deficiency disease or a weakened state of immunity.
Two technologies that are currently employed to reduce biological contaminant or pathogen levels in powdered food products are: (1) exposing the food products to chemical agents in gaseous form; and (2) irradiating the food products. It has been found that treating food products with gaseous chemical agents may adversely impact the food product's final quality and, in some instances, may even contaminate the food product. As a result, the industry has now focused on the process of irradiating food products to reduce biological contaminant and pathogen levels.
Irradiation technology for food sterilization has been scientifically understood for many years dating back to the 1940's. An increasing concern for food safety and effective medical sterilization has recently resulted in expanded government regulatory approval of irradiation technology for food processing. Because irradiation has proven to be an effective means of reducing the population of harmful biological contaminants and/or pathogens, United States Government regulatory agencies have approved the use of irradiation processing of various foods.
The three approved sources of ionizing radiation for irradiation food processing are (1) gamma rays (typically formed by radioisotopes of cobalt or cesium); (2) x-rays; and (3) beams of accelerated electrons (i.e., e-beams). With respect to x-rays and e-beams, the U.S. Government has mandated maximum allowable energies for food irradiation. By maintaining the energy at or below the mandated maximum energy levels, effective irradiation of the food product may be achieved without causing surrounding materials to become radioactive and without destroying beneficial characteristics/properties of the food products. The currently established maximum allowable energies for x-rays and e-beams are 5 million electron volts (MeV) and 10 MeV respectively.
While the use of gamma source radiation for food irradiation purposes is simple and effective, it is also expensive and hazardous to handle, transport, store and use. In comparison, e-beam and x-ray irradiation processing require relatively little equipment and shielding, can be brought within close proximity of manufacturing lines, and can be turned on and off as needed. For these reasons, e-beam and x-ray irradiation have become the preferred technologies for food product irradiation.
The ionizing radiation provided by e-beams is in the form of electrons. In the case of x-rays, the ionizing radiation is typically provided by photons. Because photons have no mass, the photons produced by x-ray sources are able to penetrate deep into materials. However, because electrons have a small mass, the electrons provided during e-beam processing have a more limited penetration depth.
Existing e-beam and x-ray irradiation systems employ electron accelerators to either emit high velocity electrons directly for irradiation or to cause high velocity electrons to collide with a metal conversion plate which results in the emission of x-rays. A number of electron acceleration techniques have been developed over the past several decades including electrostatic acceleration, vacuum pumped cylindrical accelerators, and linear accelerators.
Over the past decade, substantial efforts have been undertaken to develop systems and methods that can safely and effectively irradiate food products in an industrial setting. However, in an industrial setting, a number of competing goals exist, such as: (1) maximizing throughput of the food product; (2) guaranteeing effective and safe levels of irradiation of the food product; (3) minimizing costs associated with the irradiating process; and (4) protecting personnel from radiation exposure.
In order to protect personnel from radiation exposure, food irradiation often takes place in a sealed area, which effectively contains the radiation. Existing systems achieve this goal by incorporating automated means for delivering the food to the radiation source, thereby eliminating direct human intervention and the associated shutdown and startup times. Thus, large-scale application of food irradiation requires an apparatus and method to deliver large quantities of food to the radiation means, without direct human intervention, and on a continuous basis.
A number of irradiation systems have been developed for industrial irradiation processing of food products. Examples of such systems are disclosed in U.S. Pat. No. 6,653,641, (Lyons et al); U.S. Pat. No. 6,096,379, (Eckhoff); U.S. Pat. No. 5,008,550, (Barrett); and U.S. Patent Application Publication No. 2002/0162971, (Koeneck et al). However, existing food irradiation systems suffer from a number of drawbacks, especially when used to process fluent food products.
Conveyor-type irradiation processing systems are either incapable of processing certain fluent products, such as liquids or gases, or are inefficient in exposing the fluent food product to sufficient and/or consistent dose(s) of radiation due to shifting of the fluent food product on the conveyor belt. When fluent food products, such as powders and granular materials, are placed on conveyor-type systems for irradiation processing, changes in the speed and/or direction of the conveyor belt tend to shift the fluent food product, resulting in the food product having an inconsistent depth during radiation exposure. Variations in the depth of the fluent food product affect the actual dose of radiation to which an amount of fluent food product receives, especially during e-beam processing where penetration depth is limited. For example, increasing the depth of the fluent food product results in the radiation being unable to penetrate the fluent food product and sufficiently irradiate the fluent food product adjacent to the conveyor belt. As a result, the same food product may have to be subjected to the radiation energy numerous times. This negatively affects product throughput.
Existing radiation processing systems compensate for inconsistencies in the actual dose of radiation that fluent food product receives by applying the radiation energy at increased power or dosage levels to ensure that all of the fluent food product actually receives a sufficient dose of radiation. Typically, these increased power or dose levels are on the magnitude of 2-5 times greater than a target power or dose level that would theoretically deliver the sufficient dose of radiation energy to the fluent product. In other words, the radiation energy is applied at a theoretically sufficient target power or dose multiplied by a safety factor of 2-5. Greater power and dose levels result in increased energy consumption, increased propessing costs, and, in some instances, undesirable heating of the fluent food product.
A further drawback of existing radiation processing systems is that they typically use linear shaped irradiation chambers. Typical sources of radiation, however, produce radiation energy in radiant patterns. Thus, as the food product passes through these linear irradiation chambers, the radiation energy strikes the food product at a normal angle for only a short period. This results in a less than optimal transfer of radiation energy to the food product, resulting in an increased amount of power being used to effectuate exposure to a sufficient radiation dose.